Method of obtaining crystallized sugar from wood sugar solutions



Patented July 16, 1935 UNITED STATES PATENT OFFICE METHOD OF OBTAINING CRYSTALLIZED SUGAR FROM WOOD SUGAR SOLUTIONS Friedrich Koch, Heidelberg, and Hugo Koch,

Mannheim-Rheinau,

Germany, assig'nors to No Drawing. Application April 6, 1934, Serial No. 719,402. In Germany April 7, 1933 12 Claims.

The object of the present-invention-is to make it possible to bring about the crystallization of material such as glucose or xylose from a mixture of sugars, carbohydrates, or organic substances such as results from the acid treatment and hydrolysis of vegetable material such as wood. The invention is based upon the discovery that it can be made possible, by observing certain special conditions, to effect the crystallization in inverted form of sugars obtained from ligneous vegetable tissues by acid hydrolysis. The material with which the present invention is concerned is of a nature very different from that which is involved in the crystallization of glucose from solutions formed by the hydrolysis of starch, for example. The analytic composition of sugar from ligneous matter differs materially from that of starch sugar. Whereas, for example, a starch sugar suitable for crystallization consists practically entirely of glucose, except for a small, relatively immaterial amount of polymeric sugar (dextrins) and organic material, sugar derived from the wood of conifers may be said to contain in round figures 65% glucose, 17% mannose, 10%

xylose, several percent fructose, galactose, polymeric sugars, organic substances, and uronic acids. Add to this the fact that due to the method of making the wood sugar solution in the first instance theproduct contains a materially higher content of inorganic impurities than is the case with starch sugar. Finally, in the case of the wood sugars, the raw material from which the sugar solutions are obtained has a marked bearing on the analytical composition of the result- 35 ing carbohydrates. In other words, the analytical composition of the carbohydrates obtained from a treatment of coriifers is materially different from that which is obtained from the treatment of foliaceous trees. In working up the wood sugar solutions to crystallizable glucose and xylose, the progress of development in the crystallization process is materially aflected by the various varieties or types of sugar and other constituents. Whereas it is accordingly very difficult to isolate the glucose by itself in sufficient purity, it has been found that by observing certain particular relations between the different types of sugar contained in the mixture, crystallization 50 may be made to proceed very satisfactorily. In this connection .it was particularly important to discover those mixtures which would not only be most favorable to crystallization but in which the physical properties of the crystal masses would also permit of a simple and easy manipulation of the impure solutions to cause them to yield pure products.

According to the present invention the mannose content is so regulated that a crystalline mass is obtained which in spite of high sugar concentration at ordinary temperature, does not rigidify (as for example in the case of starch sugar of comparable content in reducing sugars) but retains a certain pasty consistency by reason of which a complete pressing-oii of the mother liquor as in a filter press or high-pressure press, or a removal of the same in a centrifugal separator is made possible.

In pressing out a crystalline mass in whose mother liquor hydrolyzed hemicellulose, particularly mannose, is present, the efficiency of the pressing operation can be materially increased by raising the temperature during the course of the operation slowly up to about 80 C. Due to the presence of the hemicellulose components it is possible to obtain a hard, pure, press cake without having the crystals go into solution in the viscous mother liquor due to the increase in temperature. The pressing operation can be carried to such an extent that at the end the kind of sugar which is crystallized remains behind in the form of hard plates substantially free from mother liquor. The following table shows the eifect exerted by temperature during the pressure of the crystals on the sugar content and on the removal of inorganic material (ash contents) other conditions being the same.

Press cake obtained Temperature during pressing Glue se Chloride hydrate contents 83% 0.6% 01 86% 0.3% CI 88% 0.1% Cl 90% 0.06% 01 bined with sugar from deciduous trees which is low in mannose in such a manner that in the crystallizing syrup the mannose, together with the other foreign kinds of sugar, is'present to the extent of about 5% to 10% of the total sugar. This percentage of foreign sugar sufiices to prevent a setting of the crystal pulp even with a high sugar concentration and to permit of a clean pressing-out of the non-crystallizing mother liquor together with its associated impurities.

It is also possible to reduce the high content of mannose to the desired point in sugars obtained from conifers by a preliminary and only partial decomposition of the wood. In this case the wood, prior to its complete saccharificationis so extracted with dilute acid or alkalies that the easily hydrolyzed hemicellulose which in round figures consists of 50% mannose, is removed.

When this is followed by saccharification of the previously extracted wood a sugar containing approximately only 8% mannose is obtained.

When wood from foliaceous or deciduous trees is treated to obtain crystallized glucose, the main portion of the pentoses can first be removed by means of a preliminary graded saccharification. When the wood which remains is thereupon subjected to complete saccharificatiomit may then yield solutions in which the content of foreign kinds of sugar is too small to attain the described effect. In such cases, therefore, mannose, which, for example, may be obtained from the partial saccharification of woods poor in pentose content, may be added to the necessary extent. The combination may also be effected by subjecting mixtures of the different preliminarily treated kinds of wood to conjoint saccharification. By way of example, the wood sugar solutions containing 5% mannose and a small proportion of other companion substances, are well adapted to the treatment for obtaining glucose crystals. To this end it is possible to make use of wood sugar derived by methods such as described in United States Patents Nos. 1,544,149, 1,678,819, or 1,599,462 for the production of a syrup which has a sugar concentration of for example 65% to 75%. In this case it is not necessary to have a degree of purity of the sugar solution so high that the dried substance contains over 90% glucose. The syrup may be inoculated with some pure glucose hydrate or anhydride. The amount added for inoculation may be about 1% for example of the total sugar. Crystallization then is allowed to proceed at somewhat elevated temperature under slow stirring.

If, example, the starting material contains 100 kilogr. of wood sugar in the condition of a 70% syrup which contains 5 parts of mannose and about 3 parts of galactose-like sugar and chlorides representing 0.8% of chlorine, there is obtained by crystallization accompanied by stirring 55 kilogr. of glucose free from all other kinds of sugar and with a chloride content representing only 0.025% of chlorine.

In the production of hydrous glucose the temperature of crystallization with a sugar concen-' tration of for example 65%, may be 40 C. on the first day, 38 C. on the second day, and 35 C. on the third day. In the production of glucose anhydride with a sugar concentration of the temperature may for example be held at 50 C. After crystallization has progressed to the stage at which a thick crystal pulp is formed the mass may be centrifuged. The well developed prismatic crystals can be readily freed from adhering mother liquor by washing with a small quantity of water. -This washing can be carried out without material loss of sugar as the mother liquor is readily soluble and does not tend to after-crystallize. For these reasons it is also possible to remove the relatively large amount of inorganic components in a single crystallizing operation, if, as stated, the crystallization is undertaken in the presence of 5% to 10% of foreign sugar, specially mannose.

If the mannose content is reduced to below 5% a more speedy crystallization of much harder crystals results. By increasing the mannose content to about 10%, the fluidifying effect is increased. The following results of experiments show the influence of the mannose content in wood sugar on the yield and character of the crystals obtained:

Yield in crystals Mannose contents Character of the crystals Percent Percent 17 35 Soft; filterable.

Semi-solid; pressable.

Solid; pressable.

Very solid; pressablc under high pressure. Hard; not pressable.

. with the desired content of foreign sugar remains.

After re-solution of the press cake a second crystallization may be carried out under the above described conditions.

On the other hand, in the case of glucose solutions which are free from mannose, the crystal pulp at a certain stage of the crystallization rapidly assumes a consistency rendering it unsuited to subsequent treatment. Especially when the work is carried out with a high degree of concentration of sugar, it may very well happen that the mass in a very short time becomes totally stiff and rigid or, when the procedure is not conducted with sufiicient attention, it may result in small gummy crystals which make satisfactory purification impossible. These difficulties are eliminated by the presence of mannose, inwhich case. even with a high sugar concentration and without very close attention and control, readily separable and well developed crystals are obtained of a purity which shows a marked improvement as compared to the raw material. Generally speaking, the content of foreign sugars can no longer be determined and the ash contents lie within the limits permissible even for pure products.

The favorable action of mannose is also exerted in the crystallization of xylose. Here, too, mannose, together with the other forms of sugar, and sugar-like components of the wood sugar solution, permits well developed crystals to be obtained which are readily purified, whereas otherwise the crystals are small, poorly developed, tending to stick together, and then, tenaciously holding back the mother liquor,

We claim:

1. The method of preparing sugar solutions from acid-treated hydrolyzed vegetable materials in anticipation of a crystallization treatment for the recovery of glucose or xylose, which comprises causing the solutions to contain approximately 5 to 10 parts of mannose in 100 parts of total sugars.

2. The method of obtaining crystallized glucose or xylose from solutions obtained by the acid hydrolysis of vegetable materials, which consists in causing the solutions of the hydrolyzed vegetable materials to contain 5 to 10 parts approxi-- mately of mannose in 100 parts of total sugars, then crystallizing for the recovery of glucose or xylose and separating off the mother liquor.

3. The method of preparing sugar solutions from acid-treated hydrolyzed vegetable materials in anticipation of a crystallization treatment for the recovery of glucose or xylose which comprises mixing sugar rich in mannose such as is obtainable from conifers with sugar that is weak in mannose in such relative proportions as tocause the solution to contain approximately 5 to 10 parts of mannose in 100 parts of total sugars.

4. The method such as set forth in claim 1 in which the stated relation between the mannose and total sugars is brought about by a preliminary extraction from the wood of conifers prior to complete saccharification of a portion of the readily hydrolyzable hemicellulose.

5. The method such as set forth in claim 1 in which the stated relation between the mannose and total sugars is brought about by a conjoint saccharification of the wood of conifers and deciduous trees mixed in quantities to result in the stated percentage relation in the ultimate solu tion of 5 to 10% of mannose in 100 parts of total sugars.

6. The method of preparing sugar solutions from acid-treated hydrolyzed vegetable materials in anticipation of a crystallization treatment for the recovery of glucose or xylose which comprises preparing a solution containing less than 5 noncrystallizing sugars and adding thereto the easily hydrolyzable hemicellulose from material rich in mannose until thesolution is made to contain approximately 5 to 10 parts of mannose in 100 parts of total sugars.

'7. The method such as set forth in claim 2 in which the crystallization step is conducted at temperatures of from about to C. and under gentle agitation.

8 The method such as set forth in claim 2 in which the process of crystallization is initiated by inoculation with sugar of the type to be crystallized out of the solution.

9. The method such as set forth in claim 2 in which the crystallization step is conducted at temperatures of from about 35 to 50 C. and under gentle agitation until a stiff crystal mush is obtained and then separating the crystals from the mother liquor by centrifugal and washing with a small quantity of water.

10. The method of obtaining crystallized glucose or xylose from solutions obtained by the acid hydrolysis of vegetable materials, which consists in causing the solutions of the hydrolyzed vegetable materials to contain 5 to 10 parts approximately of mannose in parts of total sugars, obtaining this relation in the case of a solution which contains more than 10% of mannose by first crystallizing out at ordinary temperature, then separat-' ing the crystal mush from the mother liquor on a filter press, then redissolving, and then, having thus obtained the desired relation between the varieties of sugar in solution, crystallizing out the glucose or xylose at temperatures of from 35 to- 12. The process set forth in claim 2 in which 

